Thermoelectrical apparatus



Oct. 19, 1937. R. WILLIAMS 2,096,571

THERMOELECTRICAL APPARATUS Filed April '17. 1936 INVENTOR @k mamPatented Oct. 19,1937

UNITED STATES PATENT OFFICE 10 Claims.

The present invention deals with electrical apparatus responsive tothermal changes. More particularly my invention is directed to means andmethods for causing expansion or contrac- 8 tion of a. body, accordingto the differing degrees of heat to which it is subjected, to effectchanges in the impedance of an electrical circuit.

My invention is particularly applicable to cases where the electriccurrent causes the heating of 1. materials, which it is desirable tokeep within certain limits of temperature.

One purpose of my invention is to control the temperature of liquidswhich are heated by electrical means and to keep the temperature of suchll liquids within close limits, notwithstanding that such liquids maybesubjected to a wide variation of temperature due to their movement, forexample, through the heating chamber.

More particularly my invention is especially 2o suited for controllingthe temperature of liquids which are heated while passing through achamber, in which they may remain only a comparatively brief length oftime.

Several embodiments of my invention are as shown in the drawing hereuntoappended, where:

Fig. 1 represents one form of my invention employing an electro-magneticform of control.

Fig. 2 represents another form of my, invention where an inductor ofvariable impedance is 30 employed as the controlling element.

Fig. 3 shows a form of this invention using a variable resistor as thecontrol element.

Fig. 4 shows a form where a single element functions both as control andas heating element.

Referring now to Fig. 1 I have here shown a container it which may be ofany suitable material, in which is held, or through which passes theliquid II, which it is desired to maintain at a given temperature.

The leads i2 represent a supply of alternating current from any suitablepower source. One of these leads is directly connected to one end of aresistance element ll, which is submerged in the liquid II.- The otherend of heating element i3, is connected by a conductor H to one end ofthe winding 15, and the other end of this winding is connected to theother conductor l2, thus completing an electrical circuit wherein heaterelew meat It, and winding l5 are connected in series with one anotheracross the power source.

Element It, represents a core of any suitable magnetic material such aslaminated iron or other magnetic alloy of high permeability; This core55 is in the form of a rectangle, one of whose'sides is provided with anopening I! and which core has the winding l5 embracing one or more legs.

The element l8 represents a supporting frame work which may be made ofany suitable material of suflicient rigidity and preferably ofnon-magnetic material. This frame I! is open so as to ail'ord freecirculation for the liquid ll therethrough, and may be fastened to thecore It by any suitable mechanical device such as the clamps l8. It isdesirable that frame It and core l8 be fastened together with sufficientrigidity so that their relative position may not easily be subject tovariation.

This supporting frame It is held by cover II and is supporting a rod"which may rest upon the bottom portion of frame l8 and which may passthrough an opening in a suitable guiding member 2|, affixed to frame 18.

Rod 20 has at its upper extremity and firmly aihxed thereto a piece ofmagnetic material 2i such as iron or the same alloy of which core I. isformed.

Rod 2| may convemently be divided into two portions which are oppositelythreaded into a bushing 22, and the rotation of this bushing will serveto vary the over-all length of rod 20.

The material of which rod 20 is composed is chosen so that itscoeflicient of expansion will be greatly different from the coemcient ofexpansion of frame l8.

In the operation of this form of my invention, the values of resistancel3 and winding I! are so chosen that the current passing throughresistance ll will maintain liquid II at approximately the desiredtemperature. The effective length of rod 20 is then adjusted until thegap I! is only partially closed by element 2|. Under these conditionsthe reactance of the choke coil formed by winding l5 and core It willhave a certain value.

If the temperature of liquid ll rises, for any reason, rod 20 and frameIt immediately expand to an unequal degree. For purposes ofillustration, let us assume that rod 20 is made from a material whosetemperature coeflicient is greater than that of frame ll. Under suchcircumstances rod 20 will then tend to expand to a greater degree thanframe I8 and accordingly will cause element 2! to enter farther into theopening II. This reduction of the air gap between element 2| and core i6will cause the effective reactance of the inductor as a whole toincrease, due to the increased permeability of its magnetic circuit thusbrought about.

The increased impedance of the inductor will cause a reduction of thecurrent flowing through heating element l3, and thus tend to lower thetemperature of liquid ll, thus compensating for the increase intemperature which has been considered to have occurred previously.

A decrease of temperature in liquid II will cause the contraction of rod20, a widening of the airgap between elements 2| and IS, a decrease inthe reactance of inductor and consequent rise in current and heatingeffect of element l3.

Since the effective reactance of an inductor of the type just describedmay be very greatly changed by a relatively small air gap introducedinto its magnetic circuit, it is evident that'comparatively slighttemperature changes will cause comparatively large changes in thecurrent passing through such an inductor.

While I have shown element 2| as having a rectangular shape and theopening in core l6 as having a corresponding shape, yet it is evidentthat other forms and openings may be employed, and that by properlychoosing the form of opening, the effective response of the inductor maybe made to vary, relatively to the temperature changes, in almost anydesired fashion. For example, either a straight line or a logarithmicresponse curve may be obtained. In many cases a logarithmic response maybe desirable where the liquid H is apt to change suddenly or to a greatdegree.

Referring now to Fig. 2, chamber l0, liquid II, and heating element 13may be similar to these elements as shown in Fig. 1. The alternatingcurrent energyderived from leads l2 energizes heater l3 through acontrol element formed by a winding 30 embracing a core 3|, of suitablemagnetic material. I

In place of the straight rod 20 in the form previously described, thereis here shown an expansive element in the form of a helix 32, whoselower end is supported upon a frame 33. Frame 33 is similar in functionto frame 18 of Fig. 1 and is afiixed by any suitable mechanical meanssuch as bolt 34" to core 3| of the inductor element. Helix 32 bearsatits upper end a cylinder 35 formed partly of conducting material suchascopper.

Cylinder 35 is arranged so that its conducting portion 36 partlyembraces winding 30 of the inductor and the expansion of helix 32 willcause this conducting portion to move upwardly so as to uncover asimilar portion of winding 30, thereby increasing the effectivereactance of this wind- The forms of my invention shown in Figs. 1 and 2are applicable only to alternating current as a power source, but inFig. 3 I have shown my invention suitable for use either withalternating or direct current. In this form I have omitted the heatingchamber and liquid for purposes of clarity and the power leads I2 may beassumed to be carrying either direct or alternating current in thiscase. r

In series with the power leads and heater l3 are a series of carbonblocks 40. The frame II is fastened to the uppermost block and expansionrod 20 is interposed between the bottommost block and the bottom offrame 4!. it is assumed thatrod 20 temperature coeflicient of than thatof frame 4|.

In' this case is chosen to have a expansion much less Under suchcircumstances, an increase of temperature of the liquid in which thisdevice may be submerged, will cause frame 4| to expand to a greaterdegree than rod crease the resistance offered by the carbon blocks andthus lessen the current flowing through heater l3, thus giving thedesired regulating effect. The reverse action taking place upon a fallof temperature will be readily apparent. Conducting cups 53 allow thewires passing through holes 54 to make contact with the carbon blocks.

- Many variations of the forms of my invention herein shown will beapparent to those skilled in the art. For example the expansive elementmay be not only of the rod or helical forms shown, but may becone-shaped or spiral or of any other suitable shape. It will beapparent that a helical or spiral shape will give a greater expansionfor a given change of temperature; due to the greater effective lengththus available.

The variable inductor described may manifestly take the form of atwo-winding transformer and the variable magnetic gap of Fig. 1 may alsobe used as a shunt magnetic circuit instead of the series circuit shown.

The means for adjusting the effective length of rod 20 may take on formsother than the bushing shown in Fig. 1 and in somecases it may be deviceof an electrical nature in series with the leads l2, or heating elementl3 may be made capable of adjustment by means of suitable tapstherefrom.

In Fig. 4 I have illustrated yet another modi-' fication of myinvention, where a single element furnishes heat and at the same time isvaried by the temperature of the liquid around it so that such as arheostat, variable choke like.

If the liquid surrounding rods 5|, and being heated by carbon blocks 40,should become warmer than normal, rods 5| will expand more than willblocks 40, and accordingly the the stack of blocks 40 will decrease,thus increasor even solids may be so heated and controlled,

by making suitable modifications in the apparatus herein shown. Forexample, if the form'of Fig. 4 be used to heat gases, some shield shouldbe interposed betweenthe heating element and the expansion rods, topreventradiated heat from directly influencing these rods.

While I have shown means for adjusting the length of the expansion rodsonly in the case of Fig. 1, yet it is to beunderstood that adjustingmeans similar to those shown in Fig. 1, or of any other suitablecharacter may be provided in the case of the other forms of my inventionillustrated in the remaining figures. Likewise it is to be understoodthat the adjustments of my device for a given temperature of the liquidmay be accomplished not only by means of changing effective length ofthe expansion members, but also it may be accomplished by using anexternal electrical device such as a rheostat, choke-coil,potentiometer, or similar device.

In the form of my invention employing a magnetic controlling element, Iprefer to use some material of extremely high permeability, in order togive the greatest possible range of adjustment for the minimum motion ofthe expansion elements. In the case of the magnetic controls, it is alsopossible to make any adjustments desired by the use of an auxiliarywinding upon the same core, but carrying D. C. current. Such a windingacts to vary the permeability of the core in accordance with well knownprinciples.

It is apparent that various means may be used to magnify thethermostatic action of my device. For example, some magnifyingmechanical motion such as a lever may be interposed between theexpansion rod and the actual controlling elements, such as element 2| ofFig. 1, or element 36 of Fig. 2.

Since the expansion of the rod is small in degree, but represents aconsiderable amount of actual pressure, and since the motion of thecontrolling element proper does not call for the dispersion of anyconsiderable amount of energy, such magnifying device will not decreasethe sensitivity of response of my device. Alternatively, electricalamplifying device, may be employed between the variable impedancemember, and the heating circuit. Such amplifying devices, includingelectronic relays are well known in the art, and a further descriptionthereof is considered unnecessary.

Another modification of my invention may consist of using some form ofbi-metallic thermostatic element in place of the expansion member hereindescribed. Such ,bi-metallic element will cause a lateral motion, ratherthan the vertical motion of the expansion rod. The adaptation of such alateral motion for actuating the controlling element proper will beapparent to one skilled in the art. I

It is to be understood that the various elements shown in the form of myinvention herein illustrated, are to be suitably insulated from oneanother, so that short-circuits will not occur. For

example, in the case of the type shown in Fig. 3, it will be apparent toone skilled in the electrical art, that if rod 20 and frame II were bothconstructed of conducting material, the current would pass through thesetwo elements in series withone another, from the conducting cup I on oneend of the pile of carbon blocks, to the cup on the other end of thepile.

Accordingly it would be necessary in such case, to interpose insulationsomewhere along this short-circuiting path. For example, either one orboth cups might be insulated from contact with the expansion rod on theframe.

I claim:-

1. An electrical heating system comprising electrothermai conversionmeans placed in direct contact with the material to be heated,electrical impedance means controlling the electrical energy supplied tosaid conversion means, said impedance means including at least onemember whose continuous displacement of relative position to a veryslight degree will cause relatively large continuous variations in theelectrical value of said impedance means, a solid expansion member alsoin close thermal contact with the material to be heated and means forthermally shielding said expansion member from said electrothermalconversion means and said impedance means, and relatively short, rigidand direct mechanical coupling means uniting said displacement member ofsaid impedance with said expansion member into substantially a singleunitary structure without substantial flexure or moving joints, wherebyrelatively slight expansion or contraction movements of said expansionmember are transmitted without lost motion to said displacement memberand result in relatively large variations of the electrical energysupplied to said electrothermal conversion means.

2. An electrothermal conversion and control system according to claim 1,characterized in I that the displacement member and electrical impedancemeans lie wholly without the material to be heated.

3. A system according to claim 1, characterized in that said impedancemeans is constituted by an inductive reactance of the iron core type andthe displacement member is constituted by a portion of the core of saidimpedance, said core being of a material of relatively high magneticpermeability and said displacement member being of the air-gap type andso disposed that its movement varies the effective permeability of thetotal magnetic circuit of said core.

4. A system according to claim 1, characterized in that said electricalimpedance means is substantially entirely reactive in nature.

5. A system, according to claim 1, characterized in that said electricalimpedance means is substantially entirely resistive in nature.

6. 'I'hermo-electric apparatus including a heater, means for supplyingcurrent thereto, a thermostat of solid material responsive to theeffective thermal output of the heater, a variable reactance controlelement of the air-gap type in series with the current supply and theheater and rigid continuously effective mechanical means coupling thethermostat and the control element into a unitary structure so as toincrease the reactance thereof when the effective thermal output of theheater increases.

7. A combination heater and thermostat comprising a plurality of piecesof poorly conductive material stacked together, said material being of anature so that the effective resistance of the tivity and as a thermallyresponsive rheostat by virtue of the varying pressure exerted upon theends thereof, said stack and said expansive means having therebetweenfree space for circulation of fluid to be heated.

8. An electrical heating system comprising a variable impedance and asolid expansion element, rigid means for continuously anduninterruptedly coupling said elements into a single unitary structureso that the expansion element will continuously increase the eifectiveimpedance of the variable impedance when said expansion element issubjected to an increased temperature, and a heating element in circuitwith said variable impedance and a source of electric current and alsocomprising means for thermally shielding said impedance and saidexpansion element from one another, said expansion element and thevariable portion of said impedance being arranged linearly with respectto each other, whereby these two elements constitute a single rigid andunitary structure.

9. A combination heater and thermostat adapted to be immersed in afluid, comprising two plane surfaced blocks, thermally expansive rodsjoining said blocks substantially at their outer edges and determiningthe distance therebetween, a heater comprising a stack of blocks ofmaterial whose en'ective resistance is afunction oithe pressurethereupon, clamped between said plane blocks, and means for. afiordingelectrical connections to the respective ends of said stack, saidexpansive rods and said stack of blocks having therebetween freespaceior circulation of said fluid.

10. An electrical heater including a stack of carbon blocks immersed ina medium to be heated and means to vary the pressure upon said blocksinversely according to the temperature of said medium, said blocks andsaid pressure-varying means having therebetween free space forcirculation of said fluid medium.

ROGER WILLIAMS.

